U.S. patent number 3,946,730 [Application Number 05/219,686] was granted by the patent office on 1976-03-30 for biomedical electrode assembly.
This patent grant is currently assigned to NDM Corporation. Invention is credited to Robert Paul Monter.
United States Patent |
3,946,730 |
Monter |
March 30, 1976 |
**Please see images for:
( Certificate of Correction ) ** |
Biomedical electrode assembly
Abstract
A body electrode suitable for sensing bioelectrical potentials
and adapted to be electrically connected to an external
electrically responsive member, the body electrode including a
stainless steel electrode and an aqueous alkali metal sulfate
electrolyte; and methods of accurately receiving and transmitting
for monitoring and diagnostic purposes small electrical voltages
generated in the body.
Inventors: |
Monter; Robert Paul
(Centerville, OH) |
Assignee: |
NDM Corporation (Dayton,
OH)
|
Family
ID: |
22820326 |
Appl.
No.: |
05/219,686 |
Filed: |
January 21, 1972 |
Current U.S.
Class: |
600/392; 600/394;
600/397 |
Current CPC
Class: |
A61B
5/25 (20210101); A61B 2562/0217 (20170801) |
Current International
Class: |
A61B
5/0408 (20060101); A61B 005/04 () |
Field of
Search: |
;128/2.6E,2.1E,417,418,DIG.4 ;252/518,521 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Irons & Sears
Claims
I claim:
1. In an electrode/electrolyte assembly for use in sensing the
bioelectrical potentials of a living animal body and having means
defining a cavity opening to the body and an electrode member at
the base of the cavity and projecting therethrough, an electrolyte
substantially filling said cavity and in direct contact with said
electrode, and said electrode being adapted to be electrically
connected to an external electrically responsive member, the
improvement wherein the electrode is stainless steel and the
electrolyte in said cavity means is an alkali metal surface.
2. The assembly of claim 1 wherein the electrolyte is an aqueous
composition containing, by weight, from about 1% to about an
aqueous saturated solution of alkali metal sulfate.
3. The assembly of claim 2 wherein the electrolyte is an aqueous
composition containing, by weight, from about 10% to about 20%
alkali metal sulfate.
4. The assembly of claim 2 wherein the alkali metal sulfate is
sodium sulfate.
5. The assembly of claim 2 including a sponge-like cellular matrix
wherein the electrolyte is an aqueous highly viscous semisolid
composition comprising, by weight, from about 1% to about an
aqueous saturated solution of alkali metal surface, and a small
amount of a water-soluble, water swellable mucilage, said
electrolyte being impedded in said sponge-like cellular matrix.
6. The assembly of claim 5 wherein the mucilage is a neutralized,
water-soluble, waterswellable carboxypolymethylene present in the
concentration of about 0.2% to about 5.0%, based upon the total
weight of the electrolyte composition.
7. The assembly of claim 5 wherein the means defining a cavity
opening of the body is a non-conductive cup member containing
therein the aqueous highly viscous semisolid alkali metal sulfate
electrolyte.
8. The assembly of claim 7 wherein the aqueous highly viscous
semisolid electrolyte composition substantially fills the interior
of said cup member and has a thickness at least as great as the
depth of said cup member.
9. The assembly of claim 8 wherein the thickness of said aqueous
highly viscous semisolid electrolyte composition exceeds the depth
of said cup member.
10. The assembly of claim 9 wherein a removable protective covering
overlies the open end of the cup member, said covering being a
sheet material having a raised portion overlying the semisolid
electrolyte protruding from the cup member, said raised portion
being spaced from said semisolid electrolyte but for a projection
engaging the protruding end of said semisolid electrolyte for
holding the semisolid electrolyte in said cup member.
11. The assembly of claim 10 wherein an aperatured flexible and
resilient sheet surrounds the generally centrally located cup
member and overlies the exterior of the closed base end thereof,
the surface of said flexible and resilient sheet in coplanar
relationship to the open end of the cup member having a pressure
sensitive adhesive coating thereon for adhering to a body surface,
and means for securing said flexible, resilient sheet to said cup
member including the stainless steel electrode which projects
through the base of the cup member and through said aperature in
said flexible and resilient sheet.
12. The assembly of claim 11 wherein the electrode projecting
through the base of said cup member base and the aperture in said
flexible, resilient sheet is a conductive metal snap fastener, that
portion of which in contact with the electrolyte is stainless
steel.
Description
BACKGROUND OF THE INVENTION
While biomedical instrumentation experts have long appreciated the
diagnostic and monitoring value of bioelectrical potentials
originating from, for example, the heart of a patient victimized by
a myocardial infarction, accurately receiving, transmitting and
recording the small voltages involved has never been an easy
matter. Clinicians, general practitioners and specialists are all
very much aware of the frustrations attending faulty recordings
caused by motion artifacts, spurious electrical signals, corrosion,
poor electrolyte stability, high skin impedance, and the like.
What with man now taxing his strength and endurance more and more
at supersonic speeds, in aerospace explorations and in excursions
to ocean depths, significantly increased reliance is placed on
monitoring equipment and under greatly differing conditions. It is
getting more important, for example, to provide electrodes which
are versatile and reliable and which may be used almost as
effectively with an active subject as with an immobilized person.
Not only must the electrode fastened to the subjects's body be
firmly secured for proper and accurate functioning, but it is
necessary that the quantity of interposed electrolyte be such that
it uniformly coats a predetermined area of the skin. Furthermore,
this uniformity must be maintained throughout the recordings.
Also, both the comfort of the subject and the avoidance of
distortions in, for example, electrocardiograms require that the
electrolyte or electrode assembly should not irritate the skin even
during prolonged contact.
Of course, the electrolyte must be of such a nature and composition
that when in contact with the electrode it is electrically stable,
i.e., it should provide good performance, such as low and stable
offset voltages and low impedance throughout its use. It should not
deteriorate, dry up or deleteriously affect the electrode. Nor
should it be so viscous as to fail to adequately penetrate the
skin. In short, storage stability or good shelf-like are very
desirable.
Obviously, some very stringent requisites are being placed on body
electrodes of the type contemplated herein. The search persists for
improved electrode assemblies, as is evident from the following
references which are deemed of interest: U.S. Pat. Nos. 3,027,333;
3,048,549; 3,170,459, 3,265,638; 3,420,223; 3,487,827; 3,567,657;
3,590,810; 3,607,788; "Principles of Applied Biomedical
Instrumentation", by L. A. Geddes & L. E. Baker, 1968, pp.
208-9 and 243-245.
U.S. Application Ser. Nos. 11,208 and 103,498, now U.S. 3,701,346
patented Oct. 31, 1972, described in detail electrode assemblies of
the type contemplated herein, particularly the latter application
which is incorporated herein by reference and teaches a pre-filled
electrode assembly essentially as shown in the drawing of the
instant application.
It is the primary object of the present invention to provide a very
unique and versatile electrode/electrolyte assembly having
extremely desirable properties, included among which are a accuracy
and reliable bioelectrical conductance.
THE INVENTION
The present invention relates to a novel body electrode and its use
in sensing the bioelectrical potentials of a living animal body.
More particularly the instant discovery concerns an
electrode/electrolyte assembly wherein the electrode is made of
stainless steel and the electrolyte is an aqueous alkali metal
sulfate composition.
According to a more specific and preferred embodiment the
electrolyte is an aqueous composition having an alkali metal
sulfate concentration in the range, by weight, of about 1% upto
about the saturation point of alkali metal sulfate in water.
Preferably a small but effective amount of a water-soluble,
water-swellable mucilage is present in the aqueous alkali metal
sulfate solution to provide a viscous electrolytic mixture which,
according to a still further embodiment, is absorbed by a
sponge-like cellular matrix to provide a highly viscous semisolid
electrolyte composition.
While a concentration of alkali metal sulfate in the range of about
1% to about the saturation point in water may be employed, a
concentration in the range of about 10% to about 20%, by weight, is
preferred.
Typical alkali sulfates within the purview of the present invention
are the alkali metal sulfates, such as sodium, potassium and
lithium sulfates.
Among the water-soluble, water-swellable mucilages (also known as
gelling aids and water-soluble resins) useful herein are
carboxymethylcellulose, polyvinyl alcohols, cellulosic gums,
polymethylene oxide, sodium alginate, gum tragacanth, polyacrylic
acids, such as those hydrophilic, high viscosity, polyacrylic acids
having a molecular weight of about (1) million to about (6) million
and useful in cosmetic and pharmaceutical preparations, e.g., the
Carbopol water-soluble resins. (Carbopol is a trademark used by B.
F. Goodrich Chemical Co.)
Best results are achieved with the polyacrylic acids by
neutralizing same with any of a number of neutralizing agents, such
as the fairly strong organic and inorganic bases, including but not
limited to NaOH, KOH, NH.sub.4 OH, alkyl amines (mono-, di-, and
tri-), alkanol amines (mono-, di-, and tri-), such as
triethanolamine, triamylamine, dodecylamine, di(2-ethylhexyl)amine,
and the like.
The resulting neutralized mucilage is usually present in the
concentration of about 0.2% to about 8.0% preferably from about
0.85% to about 5.0%, by weight, based upon the total weight of the
electrolyte composition.
If desired, conventional additives, such as mold inhibitors and the
like, may be present in small quantities, usually less than about
1%. For example, very desirable results are achieved with
chlorinated aromtic hydrocarbons, including
2-chloro-meta-5-xylenol, salts of organic acids, such as sodium
benzoate, etc.
While the blending sequence of the electrolyte components admits of
numerous variations, it is desirable and preferred to make the
aqueous alkali metal sulfate solution separately and add thereto,
with adequate stirring, the mucilage component which may then be
neutralized in situ. The mold inhibitor or the like, if any, is
preferably introduced with the neutralizing agent for more
effective disbursement.
Generally, the electrolyte components are blended at ambient
temperature and atmospheric pressure. If desired, for example,
elevated temperatures and corresponding diminished pressure
conditions, and vice versa (within the inherent tolerances and
physical properties of the components) could be used very
satisfactorily.
To better understand the present invention a preferred embodiment
utilizing essentially the structure of U.S. application Ser. No.
103,498 heretofore alluded to and incorporated herein by reference
will be described in some detail.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a perspective view of a protective covering for an
electrode.
FIG. 2 is a cross sectional view of the electrode and protective
covering taken along line 2-2 of FIG. 1.
FIG. 3 is a partially exploded perspective view of the underside of
the electrode with the protective covering removed.
DESCRIPTION OF A PREFERRED EMBODIMENT
The drawing illustrates an electrode, generally designated 10,
consisting of a circular flexible and resilient sheet 12 overlying
a centrally located, inverted cup member 14 and sandwiched between
a clamp plate 16 located on top of the sheet 12 which is of the
same form and in alignment with the inverted cup member 14. The
inverted cup member 14 is in the form of a cavity washer having a
circular flat base with a semi-circular or U-shaped annular flange.
The diameter of the cup member 14 is substantially greater than its
height. These parts are held together by a metallic conductor
formed from a male snap fastener member, generally designated 18,
and which includes a lower, circular plate portion 20, from the
center of which a hollow stud 22 projects upwardly, and an upper
plate portion 24 having an upwardly protruding hollow socket
portion 26 receiving the stud 22.
The parts are assembled and held together by centrally locating and
aligning the cup member 14 and the clamp plate 16 on opposite sides
of the sheet 12. The stud 22 is then inserted through aligned
apertures in the centers of the sheet 12 and the members 14 and 16
and into the socket 26. The pressing together of the snap fastener
portions causes the upper end of the stud 22 to fold inwardly and
its side walls to collapse outwardly whereupon the snap fastener
parts are tightly wedged together.
The bottom surface of the sheet 12 has a commercially available,
medical grade acrylic pressure sensitive adhesive coating 28. Until
the electrode 10 is to be used, the adhesive coating 28 is covered
by a protective paper sheet 30 having a release coating on its face
which engages the adhesive coating 28.
The sheet 12 is preferably formed of a foamed plastic, such as
polyvinyl chloride, which provides for adequate aeration or
ventilation of the skin. Such a sheet is quite flexible, readily
conforming to skin contours and permitting free movement of the
skin to which it is applied. The cup member 14 may be vacuum formed
from a thermoplastic sheet material which is slightly flexible but
sufficiently rigid to prevent its collapse. A variety of plastic
materials may be used to form the cup member 14, examples being
vinyl, linear polyethylene, and cellulose acetate butyrate.
The electrolyte is preassembled with the electrode 10 by soaking a
disc-shaped sponge-like cellular matrix 32 of non-conductive,
open-cell material with an electrode jelly. The sponge-like matrix
32 preferably has a diameter substantially equal to the diameter of
the base of the cup member 14 and a thickness greater than the
depth of the cup member 14. It is sufficiently heavily laden with
electrode jelly that, when the electrode 10 is pressed on the skin,
the jelly fills the entire volume of the cavity between the skin
and the conductive plate portion 20 whereupon good electrical
contact between the skin and the conductor plate portion 20 through
the jelly is assured.
The sponge-like matrix 32 may be manufactured from open-cell
polyurethane foam material although other cellular materials would
be suitable. The sponge-like matrix 32 may be soaked with the jelly
(e.g., sodium sulfate) by immersing it in a quantity of jelly,
squeezing it under pressure and then gradually releasing the
pressure before removing it from the jelly in the same manner that
one would load a sponge with water. Of course it could be soaked
with jelly by other methods.
Since wetted by the jelly, the soaked sponge-like matrix 32 tends
to adhere to the conductive plate portion 20 and the base of the
cup member 14. The adhesion is sufficient that the soaked
sponge-like matrix 32 may simply be placed into position on the
conductive plate portion 20 and the cup member 14 without the use
of additional adhesives. When so placed, the electrode 10 is ready
for use.
Further in accordance with this invention, a protective cover 38 in
FIGS. 1 and 2 is provided for the cup member 14 and the jelly
soaked sponge-like matrix 32 so that the electrode 10 may be stored
ready for immediate use. The cover 38 comprises an essentially flat
strip of non-conductive plastic sheet having circular flat ends 40
and a raised center portion 42 formed as a cylinder, the inner
diameter of which is substantially the same as the outer diameter
of the cup member 14. The height of the cylindrical center portion
42 is greater than the combined height of the cup member 14 and the
pad 32 whereupon the inside base surface, designated 44, of the
center portion 42 is spaced from the pad 32. However, the base of
the center portion 42 has a centrally located, inwardly directed
conical projection 46, the lowermost end of which is spaced from
the plane of the protective sheet 30 by considerably less than the
thickness of the sponge-like matrix 32. For reasons discussed
below, the projection 46 is so designed that, when the parts are
assembled, the area of contact between the projection 46 and the
sponge-like matrix 32 is considerably less than the combined area
of contact between the sponge-like matrix 32 and the conductive
plate portion 20 and the base of the cup member 14.
The cover 38 is assembled on the back face of the sheet 30 with the
cylindrical center section 42 slipped over the cup member 14. The
protective cover 38 serves not only to prevent soiling of the
sponge-like matrix 32 but also, because the conical projection 46
engages the sponge-like matrix 32, it holds the sponge-like matrix
32 firmly in the cup member 14 and against the conductive plate
portion 20. When the electrode 10 is to be used, the protective
sheet 30 is merely peeled away from the sheet 12, taking with it
the protective cover 38.
EXAMPLES
The present invention will best be understood from the following
examples in which, unless otherwise indicated, percentages and
parts are by weight.
Example I
The following components are blended into an electrolyte
composition:
93.3 parts water
2.0 parts Carbopol* 940
1.6 parts triethanolamine
0.1 part 2-chloro-m-xylenol
3.0 parts sodium sulfate (anhydrous)
The anhydrous sodium sulfate is dissolved in water with mild
stirring and the polyacrylic acid is then slowly sifted into the
aqueous sall solution with rigorous stirring until the polyacrylic
acid is homogeneously dispersed and/or dissolved. A solution of the
triethanolamine and 2-chloro-m-xylenol, which is prepared by mild
heating and stirring of the two components, is rapidly added to the
mixture (with rigorous stirring and following the method used just
above for polyacrylic acid). Rigorous stirring is continued for
10-60 minutes until the proper viscosity is obtained.
Example II
The following components are blended into an electrolyte
composition:
79.1 parts water
2.4 parts Carbopol 940
3.0 parts triethanolamine
0.5 part 2-chloro-m-xylenol
15.0 parts sodium sulfate (anhydrous)
Blending is carried out essentially as in Example I, above, with
the exception that 2-chloro-m-xylenol and triethanolamine are added
(after the polyacrylic acid) separately and sequentially with
vigorous stirring upon each addition.
Example III
The following components are blended into an electrolyte
composition essentially as taught in Example I, above:
74.3 parts water
2.4 parts Carbopol 940
3.1 parts triethanolamine
0.2 part 2-chloro-m-xylenol
20.0 parts sodium sulfate (anhydrous)
The electrolyte composition of each of the above examples exhibited
the following very desirable properties when used to soak a
sponge-like cellular flexible polyurethane matrix and the resulting
semisolid composition tested by placing same in a body electrode of
the type shown in FIGS. 1 to 3 of the drawing:
In the first place, electrodes thus prefilled did not - quite
surprisingly corrode even after months and months; NaCl/stainless
steel prefilled electrodes corroded in a matter of days,
particularly those NaCl electrolytes having greater than isotonic
concentrations of NaCl. Of course, any corrosion leads to very
undesirable electrical artifacts.
The above examples also provide an electrode/electrolyte system
which exhibits very low skin impedance, yet even after prolonged
contact with the skin showed no dermatological effects.
Prior art emphatically and repeatedly points out that stainless
steel is a poor choice of metal conductor to use in sensing
bioelectric potentials. The art indicates that the use of stainless
steel results in high, variable erratic offset potential causing
distorted wave forms and base line drift in electrocardiographic
and encephalographic monitoring, particularly with monitoring
equipment of low input impedance. It has been found, pursuant to
the present invention and quite surprisingly, that the stainless
steel/alkali metal sulfate electrode system prepared as in the
above examples and otherwise taught herein achieves not only lower
but stable offset potentials, thus, resulting in a highly desirable
bioelectrical sensing system.
Pursuant to statutory requirements, there are described above the
invention and what are now considered its best embodiments. It
should be understood, however, that the invention can be practiced
otherwise then as specifically described, within the scope of the
appended claims.
* * * * *